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From Hitman's Pontiac Trans Am:
Pontiac Trans Am Page | 1978 Pontiac Trans Am
Parts | Carb Rebuild | Rear Gears | Hoses | Valve Cover | Oil Change | Transmission | Shaker Scoop | Window Runs | Stereo | Power Steering | Coil Springs | Heater Core | Front Brakes | Rear Brakes | Master Cylinder | Bleeding the Brakes | Storing the Car | Cosmetic Changes | Exhaust System | Coolant System | Snowflake Rims | Idler Arm | Rear Leaf Spring | Leaning Seats | Headliner
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Bleeding the Brakes
Ok, now that I have replaces the rear brakes, the front brakes, and the master cylinder, it is time to bleed the braking system. This is not too bad as long as you have two people to do it. The first thing that I have to tell you about is the Combination valve that is located right under the master cylinder. This valve does three things (hence the name "combination"). First, it cuts down on the pressure in the front brakes in order to build up enough pressure in the rear brakes to balance the braking system out. The second thing that it does is release pressure on the rear brakes in heavy deceleration to prevent the rear brakes from locking up and losing control of your vehicle. The third thing that it does is contain a switch that if there is pressure loss in either the front or the rear brake lines, it slides a piston either to the front or back which contacts a switch to turn on the brake light inside your car to let you know that there is a problem. If this light comes on, then you know that there is a problem with either your front or rear brakes. When you are done bleeding the brakes, this switch should center itself back out (like in my case). If it doesn't, and the light stays on, you need to do it manually. More on that later on. Ok, so now you know about the combination valve. There is a pin located on the end of the valve that you need to keep depressed in while bleeding the brakes. This pin keeps the braking system open and allows you to correctly bleed the brakes. If you don't hold this pin in, then it shuts of the front brakes because it feels that there is an imbalance in the system. I just used a c-clamp to hold this open while I did the brakes. Now, what you want to do is make sure that there is enough fluid in the reservoir at all times while you do this. Keep the lid on the master cylinder, but don't use the clamp on the top of it. You just want to keep brake fluid from splashing anywhere, and make sure you keep checking the fluid level!
You want to start with the shortest line and work your way away from the master cylinder. Start at the drivers front brake, then work to the passenger front brake, then to the drivers rear brake and finally the passengers rear brake. This is where having two people comes in handy. Have one person sit inside the car to pump the brakes when you tell them to. Start at the drivers front brake and use a clear plastic tube and a clear bottle filled with brake fluid so that you can see when all of the air is out of the lines. Attach the clear plastic tube (and yes, I know the one in the picture is black, but that is all I had so give me a brake)(no pun intended) to the end of the bleeder valve located on the top of the calipers and feed the other end into the plastic bottle. Open the valve and have the person inside the car start to slowly "pump" the brakes You will see (and maybe hear) air being pushed out of the system. The plastic bottle filled with brakes fluid is there so that when the person releases the brake pedal, fluid is sucked back in instead of air. Once you see only fluid coming out, have the person push slowly on the brake pedal as you close off the bleeder valve. Make sure you close off the valve before he reaches the floor and releases the brake pedal. Now repeat this step on the front passengers side of the car. The rear brakes work the same way. the bleeder valve for the rear brakes is located behind the drum just above the brake line where it enters the wheel cylinder. Make sure you keep checking the reservoir to keep enough fluid in there to prevent air from entering the master cylinder. If this happens, you must start all over again and you don't want to do that. Do this to all 4 tires and the brake pedal should now be firm and difficult to push in (as long as the car is off.... which it should be.... I guess I should have said that from the start is that all of the bleeding is done with the car off). Anyway, as long as the brake pedal is firm you should be done. If the pedal is still soft and mushy, then there is probably still air in the system. Either you didn't bench bleed the master cylinder correctly, or the is air somewhere in the system. If the brakes are firm, you can now remove the c-clamp from the combination valve. Now you should be able to turn the ignition key on and see if the brake light went out. If it didn't, leave the key on (not car started) and you have to do it manually. To do this you need to recenter the switch by starting with the front driver caliper first. Have someone SLOWLY push on the brake pedal as you open the front bleeder valve, the light should slowly go out. Make sure you close the valve before they release the pedal so that you don't introduce air back into the system. If the light doesn't go out, then the switch must be pushed the other way. Once again, have someone SLOWLY push on the brake pedal as you open the bleeder valve on the drivers rear brake and the light should slowly go out and the switch should be re-centered. And now your done.
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